Frequent monitoring of patients permits the patients' physician to detect worsening symptoms as they begin to occur, rather than waiting until a critical condition has been reached. As such, home monitoring of patients with chronic conditions is becoming increasingly popular in the health care industry for the array of benefits it has the potential to provide. Potential benefits of home monitoring are numerous and include: better tracking and management of chronic disease conditions, earlier detection of changes in the patient condition, and reduction of overall health care expenses associated with long term disease management. The home monitoring of a number of diverse "chronic diseases" is of interest, where such diseases include diabetes, dietary disorders such as anorexia and obesity, respiratory diseases, AIDS and other chronic viral conditions, conditions associated with the long term use of immunosuppressants, e.g. in transplant patients, asthma, chronic hypertension, chronic use of anticoagulants, and the like.
Of particular interest in the home monitoring sector of the health care industry is the remote monitoring of patients with heart failure (HF), also known as congestive heart failure. HF is a syndrome in which the heart is unable to efficiently pump blood to the vital organs. Most instances of HF occur because of a decreased myocardial capacity to contract (systolic dysfunction). However, HF can also result when an increased pressure-stroke-volume load is imposed on the heart, such as when the heart is unable to expand sufficiently during diastole to accommodate the ventricular volume, causing an increased pressure load (diasystolic dysfunction). In either case, HF is characterized by diminished cardiac output and/or damming back of blood in the venous system. In HF, there is a shift in the cardiac function curve and an increase in blood volume caused in part by fluid retention by the kidneys. Indeed, many of the significant morphologic changes encountered in HF are distant from the heart and are produced by the hypoxic and congestive effects of the failing circulation upon other organs and tissues. One of the major symptoms of HF is edema, which has been defined as the excessive accumulation of interstitial fluid, either localized or generalized.
HF is the most common indication for hospitalization among adults over 65 years of age, and the rate of admission for this condition has increased progressively over the past two decades. It has been estimated that HF affects more than 3 million patients in the U.S. (J. B. O'Connell et al., J. Heart Lung Transpl. (1993) 13(4):S107-112).
In the conventional management of HF patents, where help is sought only in crisis, a cycle occurs where patients fail to recognize early symptoms and do not seek timely help from their care-givers, leading to emergency department admissions (Miller, P. Z., 1995, "Home monitoring for congestive heart failure patients," Caring Magazine, August 1995: 53-54). Recently, a prospective, randomized trial of 282 patients was conducted to assess the effect of the intervention on the rate of admission, quality of life, and cost of medical care. In this study, a nurse-directed, multi disciplinary intervention (which consisted of comprehensive education of the patient and family, diet, social-service consultation and planning, review of medications, and intensive assessment of patient condition and follow-up) resulted in fewer readmissions than the conventional treatment group and a concomitant overall decrease in the cost of care (M. W. Rich et al., New Engl. J. Med. (1995) 333:1190-95). Similarly, comprehensive discharge planning and a home follow-up program was shown to decrease the number of readmissions and total hospital charges in an elderly population (M. Naylor et al., Amer. College Physicians (1994) 120:999-1006).Therefore, home monitoring is of particular interest in the HF management segment of the health care industry.
Another area in which home-monitoring is of particular interest is in the remote monitoring of a patient parameter that provides information on the titration of a drug, particularly with drugs that have a consequential effect following administration, such as insulin, anticoagulants, ACE inhibitors, .beta.-blockers, etc.
Although a number of different home monitoring systems have been developed, there is continued interest in the development of new monitoring systems. Of particular interest would be the development of a system that provides for improved patient compliance, ease of use, etc. Of more particular interest would be the development of such a system that is particularly suited for use in the remote monitoring of patients suffering from HF.
Relevant Literature
Monitoring systems are described in U.S. Pat. Nos. 5,241,965; 5,549,117; 5,584,297; 5,307,263; 4,803,625; 4,546,436; 5,007,429; 5,019,974; 5,077,476; 5,182,707; 4,838,275; as well as in Capone et al., Am. Heart J. (1988) 116: 1606; Chadda et al., Am. Heart J. (1986) 112: 1159; Fleg et al., Arch. Intern. Med. (1989) 149:393; Katz et al., Obstetrics & Gynecology (1986)68:773; Patel et al., J. Med. Sys. (1992) 16: 101.
Scientific American Medicine (Dale & Freeman eds) 1:II provides a review of heart failure, physical manifestations and methods for the treatment thereof.
Lindahl & Omata, Med. Biol. Eng. Comput. (1995) 33:27-32 provide a description of methods of assessing edema.
Other references of note include U.S. Pat. Nos.: 3,791,375; 3,890,958; 3,974,491; 4,144,749; 4,383,533; 5,052,405; 5,323,650; and 5,385,069; as well as Swedborg, Scand. J. Rehab. Med. (1977) 9:131-135; Mridha & Odman, Scand. J. Rehab. Med. (1989)21:63-39; Mridha & Odman, Med. Biol. Eng. Comput. (1986) 24: 393-398; Kushner et al., Am. J. Clin. Nut. (1986) 44: 417-424; Breytenbach, Int. J. Oral Surg. (1978) 7:386-392; Davies et al., Med. Biol. Eng. Comput. (1971) 9:567-570; Lindhal et al., Med. Biol. Eng. Comput. (1991)29: 591-597; Iwakura, Med. Biol. Eng. Comput. (1978) 16:429-436; and Starr, BPR (1980) 17:98-102.